Counter-rotating axial-flow fan device

ABSTRACT

A counter-rotating axial-flow fan device, which requires low power consumption and has an improved flow rate-static pressure characteristic, is provided at low cost. The counter-rotating axial-flow fan device includes a first axial-flow fan unit with first blades and a second axial-flow fan unit with second blades, which are connected in series. The first axial-flow fan unit includes a three-phase motor for rotating the first blades. The second axial-flow fan unit includes a single-phase motor for rotating the second blades. The first blades and the second blades rotate in a direction opposite to each other. In addition, the three-phase motor is driven by controlling the rotation speed thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a counter-rotating axial-flow fan device, which operates at high efficiency and can be produced at low cost.

2. Description of Related Art

Counter-rotating axial-flow fan devices formed of two axial-flow fan units with a plurality of blades are well known. The axial-flow fan units include motors as a driving source and are stacked in an axial direction. In this case, the blades of one of the axial-flow fan units rotate in a direction opposite to a rotational direction of the blades of the other axial-flow fan unit. For example, a counter-rotating axial-flow fan device is disclosed in Japanese Unexamined Patent Application Laid-Open No. 2004-278370. This counter-rotating axial-flow fan device is constructed in order to increase flow rate and static pressure more than conventional levels and includes a first single axial-flow fan unit with five front blades and a second single axial-flow fan unit with four rear blades, which are joined together. Moreover, the first single axial-flow fan unit has plural webs which are combined with plural webs of the second single axial-flow fan unit, whereby three stationary blades are formed in a housing of the counter-rotating axial-flow fan device. Another counter-rotating axial-flow fan device is disclosed in Japanese Unexamined Patent Application Laid-Open No. 2007-77890. This counter-rotating axial-flow fan device is constructed in order to increase the flow rate and the static pressure more than conventional levels and includes a plurality of front blades, a plurality of stationary blades, and a plurality of rear blades, in which the number of the front blades is N, the number of the stationary blades is M, the number of the rear blades is P, and N is the largest number and M is the least number. In addition, each of the front blades has a length L1 measured in an axial direction and each of the rear blades has a length L2 measured in the axial direction, and the length L1 is greater than the length L2.

SUMMARY OF THE INVENTION

In a conventional counter-rotating axial-flow fan devices, single-phase motor or three-phase motor is used in both driving parts of two fan units. However, when two single-phase motors are used, the flow rate is not sufficient. On the other hand, when two three-phase motors are used, the flow rate increases, but power consumption and production cost also increases. In view of these circumstances, it is an object of the present invention to provide a counter-rotating axial-flow fan device with lower power consumption and improved flow rate-static pressure characteristic at low cost.

According to the first aspect of the present invention, there is provided a counter-rotating axial-flow fan device including a first axial-flow fan unit with a plurality of first blades and a second axial-flow fan unit with a plurality of second blades. The first axial-flow fan unit includes a three-phase motor for rotating the first blades in a first direction. The second axial-flow fan unit includes a single-phase motor for rotating the second blades in a direction opposite to the first direction, and the second axial-flow fan unit is connected to the first axial-flow fan unit in series. According to the first aspect of the present invention, the production cost is reduced compared with a case of driving both of the two axial-flow fan units by three-phase motors. In addition, the flow rate-static pressure characteristic is improved compared with a case of driving both of the two axial-flow fan units by single-phase motors.

According to the second aspect of the present invention, the three-phase motor in the first aspect of the present invention may be driven by controlling rotation speed thereof. According to the second aspect of the present invention, high efficiency is obtained compared with a case of using a single-phase motor in place of the three-phase motor. The rotation speed control is a method of driving the motor so that the rotation speed of the blades is kept constant.

According to the third aspect of the present invention, the first axial-flow fan unit in the second aspect of the present invention may be arranged at a gas intake side of the counter-rotating axial-flow fan device. According to the third aspect of the present invention, the axial-flow fan unit in the gas intake side is rotated at a constant speed. Therefore, the single-phase motor of the second axial-flow fan unit in a rear side (gas outlet side) is not easily affected by changes in static pressure, whereby blowing efficiency of the single-phase motor is not greatly decreased. Thus, the blowing efficiency of the counter-rotating axial-flow fan device as a whole is improved.

According to the fourth aspect of the present invention, the first axial-flow fan unit in the third aspect of the present invention may include plural first blades and the second axial-flow fan unit in the third aspect of the present invention may include plural second blades, in which the number of the first blades is N, the number of the second blades is M, and N is greater than M. According to the fourth aspect of the present invention, the benefit of preventing a decrease in the efficiency of the axial-flow fan unit in the rear side obtained by the rotation speed control of the axial-flow fan unit in the front side (gas intake side) is further enhanced.

According to the fifth aspect of the present invention, the single-phase motor of the second axial-flow fan unit in the third or the fourth aspect of the present invention may be driven at a constant frequency and at a constant voltage. According to the fifth aspect of the present invention, the single-phase motor may be driven by a simple construction, whereby the entirety of the device may be produced at a lower cost.

According to the sixth aspect of the present invention, the three-phase motor and the single-phase motor in the fifth aspect of the present invention may be driven at the same voltage. According to the sixth aspect of the present invention, the structures of the power supplies are simplified, whereby the entirety of the device is produced at a lower cost.

According to the present invention, the counter-rotating axial-flow fan device with low power consumption and improved flow rate-static pressure characteristic is provided at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an embodiment.

FIG. 2 is a perspective view of an embodiment.

FIG. 3 is a block diagram of an electric system.

FIG. 4 is a graph showing a measured relationship between the flow rate and the static pressure and a measured relationship between the flow rate and the rotation speed.

PREFERRED EMBODIMENTS OF THE INVENTION Outline

FIGS. 1 and 2 show a counter-rotating axial-flow fan device 10 including a first axial-flow fan unit 100 and a second axial-flow fan unit 200, which are arranged in line (in series) in an axial direction. The counter-rotating axial-flow fan device draws gas from the side of the first axial-flow fan unit 100 (right side in FIG. 1) and sends the gas to the outside from the side of the second axial-flow fan unit 200 (left side in FIG. 1). That is, the counter-rotating axial-flow fan device 10 discharges the gas, which is drawn from the right side in FIG. 1, to the left side in FIG. 1. It should be noted that the gas may be any kind of gas such as air, nitrogen gas, exhaust gas, etc.

First Axial-Flow Fan Unit

The first axial-flow fan unit 100 includes five first blades 101. The first blades 101 are driven and are rotated by a three-phase motor 120 which has a structure as described below. The five first blades 101 are integrally formed with a resin hub 102. The hub 102 is a component, which is made of resin by an injection molding method, and has an approximately cup shape. The hub 102 is a component for forming a part of a rotor of the three-phase motor 120 and has a portion 102 a in the vicinity of the rotational axis at the gas intake side (right side in FIG. 1). The portion 102 a is gradually decreased in diameter toward the upstream of the gas flow path and is thereby formed into a tapered shape, providing less resistance to the gas that is drawn from the right side in FIG. 1. The hub 102 has a metal reinforcing component 103 in the form of a cup mounted inside. The reinforcing component 103 is combined with a resin boss portion 104. The boss portion 104 is attached to a shaft 105 that functions as the rotational axis.

The shaft 105 is rotatably held by a stator component 108 via ball bearings 106 and 107. The stator component 108 has an approximately cylindrical shape and has an inside on which outer rings of the ball bearings 106 and 107 are fixed. The stator component 108 is secured to a resin motor base 109. The motor base 109 is connected with an outer frame 111 with an approximately cylindrical shape, via four ribs 110. The motor base 109, the ribs 110, and the outer frame 111 are an integrally formed component made of resin. The four ribs 110 also function as stationary blades.

The stator component 108 includes a stator core 112 that is mounted at an outer circumference thereof. The stator core 112 has a similar structure as that in an ordinary three-phase motor and is structured by stacking in the axial direction plural magnetic steel sheets having a specific shape. The stator core 112 includes plural salient poles that extend in a direction away from the rotational center of the shaft 105. FIG. 1 shows tip portions of the salient poles, in the form of tip portions 113 having salient pole surfaces. A resin insulator 114 is attached on the salient poles and the salient poles are wound with a magnet wire via the insulator 114, thereby forming a stator coil 115. A rotor magnet 116 is arranged separated by a gap from the outer surfaces (salient pole surfaces) of the tip potions 113 of the salient poles. The rotor magnet 116 has a substantially cylindrical shape and is attached to an inner circumferential surface of the reinforcing component 103. The rotor magnet 116 is magnetized such that the polarity alternates in the manner of N, S, N . . . in the circumferential direction.

By supplying three-phase alternate driving current to the stator coil 115, magnetic attractive force and magnetic repulsive force are generated between the tip portions 113 of the salient poles and the magnetic poles of the rotor magnet 116, and the hub 102 rotates in relation to the stator core 112. The principle of this rotation is the same as that in the case of an ordinary three-phase motor.

Second Axial-Flow Fan Unit

The second axial-flow fan unit 200 includes three blades 201. The blades 201 are driven and are rotated by a single-phase motor 220 which has a structure described below. The three blades 201 have the same diameter as the blades 101 and are integrally formed with a resin hub 202. The hub 202 is a component, which is made of resin by an injection molding method, and has an approximately cup shape. The hub 202 is a component for forming a part of a rotor of the single-phase motor 220. The hub 202 differs from the hub 101 in the structure and has an outer diameter that is approximately constant toward the downstream of the gas flow path so as to send the accelerated gas flow straight to the left direction in FIG. 1. The hub 202 has a metal reinforcing component 203 in the form of a cup mounted inside. The reinforcing component 203 is provided with a boss portion at a central portion, and a shaft 205 is fitted into the boss portion and is thereby secured.

The shaft 205 is rotatably held by a stator component 208 via ball bearings 206 and 207. The stator component 208 has an approximately cylindrical shape and has an inside on which outer rings of the ball bearings 206 and 207 are fixed. The stator component 208 is secured to a resin motor base 209. The motor base 209 is connected to an outer frame 211 with an approximately cylindrical shape, via four ribs 210. The motor base 209, the ribs 210, and the outer frame 211 are an integrally formed component made of resin. The four ribs 210 also function as stationary blades.

The stator component 208 includes a stator core 212 that is mounted at an outer circumference thereof. The stator core 212 has a similar structure as that in an ordinary three-phase motor and is structured by stacking in the axial direction plural magnetic steel sheets having a specific shape. The stator core 212 includes plural salient poles that extend in a direction away from the rotational center of the shaft 205. The salient poles include salient pole surfaces 213 at tip portions thereof. A resin insulator 214 is attached on the salient poles and the salient poles are wound with a magnet wire via the insulator 214, thereby forming a stator coil 215. A rotor magnet 216 is arranged separated by a gap from the salient pole surfaces 213. The rotor magnet 216 has an approximately cylindrical shape and is attached to an inner circumferential surface of the reinforcing component 203. The rotor magnet 216 is magnetized such that the polarity alternates in the manner of N, S, N . . . in the circumferential direction.

By supplying single-phase alternate driving current to the stator coil 215, magnetic attractive force and magnetic repulsive force are generated between each of the salient poles and the magnetic poles of the rotor magnet 216, and the hub 202 rotates in relation to the stator core 212. The principle of this rotation is the same as that in the case of an ordinary single-phase motor.

General Configuration

The motor base 109 of the first axial-flow fan unit 100 and the motor base 209 of the second axial-flow fan unit 200 are joined, whereby the first axial-flow fan unit 100 and the second axial-flow fan unit 200 are connected in series in the axial direction. These two axial-flow fan units are connected to each other by an adhesive agent. It should be appreciated that the first axial-flow fan unit 100 and the second axial-flow fan unit 200 can be connected to each other by a fastening means such as bolts.

The blades 101 and the blades 102 rotate in a direction opposite to each other. The first axial-flow fan unit 100 driven by the three-phase motor is operated by the rotation speed control using an inverter. In this case, the rotation speed control means a control method in which the rotation speed is controlled so as to be constant regardless of changes in the static pressure. That is, the first axial-flow fan unit 100 is controlled by the inverter such that the drive frequency is adjusted so as to rotate the first blades 101 at a constant speed.

The second axial-flow fan unit 200 is driven by the single-phase motor while the rotation speed thereof is changed according to the changes of the static pressure as in a conventional control manner. That is, the second axial-flow fan unit 200 is driven under a predetermined driving condition (constant frequency and voltage of the power supply). Therefore, the rotation speed of the second axial-flow fan unit 200 is affected by the static pressure condition.

Electric System Structure

FIG. 3 shows a block diagram of the counter-rotating axial-flow fan device 10. As shown in FIG. 3, the counter-rotating axial-flow fan device 10 is formed of the first axial-flow fan unit 100 and the second axial-flow fan unit 200. The first axial-flow fan unit 100 is driven by the three-phase motor 120, and the second axial-flow fan unit 200 is driven by the single-phase motor 220. The three-phase motor 120 is incorporated in the first axial-flow fan unit 100 described in reference to FIG. 1. The single-phase motor 220 is incorporated in the second axial-flow fan unit 200 described in reference to FIG. 1.

The rotation of the rotor of the three-phase motor 120 is detected by a rotation speed detection device 301 (not shown in FIG. 1). The rotation speed detection device 301 detects the rotation such that, for example, a magnet is arranged at a rotor side and a Hall element is arranged at a stator side, and then the Hall element detects the rotation of the magnet. The rotation speed detection device 301 outputs a data signal relating to the rotation speed of the three-phase motor 120, and the output data signal is input in a three-phase power supply 303. The three-phase power supply 303 is an inverter power and controls the three-phase motor 120 based on the data signal output from the rotation speed detection device 301 so that the three-phase motor 120 constantly rotates at a predetermined rotation speed. Specifically, the three-phase power supply 303 supplies the driving current to the three-phase motor 120 by controlling and adjusting the frequency thereof so that the rotation speed of the three-phase motor 120 is constant regardless of the conditions.

For example, when the rotation speed of the three-phase motor 120 is changed due to the change in the static pressure condition or the like, this change is detected by the rotation speed detection device 301. Then, the three-phase power supply 303 adjusts the frequency of the three-phase alternate current to be supplied, based on the detection result so that the three-phase motor 120 rotates at a predetermined speed. Thus, the rotation speed is controlled so that the first axial-flow fan unit 100 rotates at a constant speed regardless of the static pressure condition. In contrast, the single-phase motor 220 is supplied with driving current with a predetermined frequency from the single-phase power supply 304 and is not controlled by rotation speed, unlike in the case of the three-phase motor 120. In this case, output voltages of the three-phase power supply 303 and the single-phase power supply 304 are preferably the same in view of synchronizing the movements of the two motors and simplifying the structures of the power supplies in addition to reducing the production cost.

Measured Results

A practical example of the present invention and a comparative example were driven under the same conditions and were thereby compared. The measured results are shown in Table 1. In this case, the fan efficiency is defined by (flow rate×static pressure/power consumption)×100%. The driving voltage was 12 V. The comparative example had the same basic structure as that of the practical example of the present invention, but the comparative example used singe-phase motors for the two axial-flow fan units. As shown in Table 1, in the practical example of an embodiment of the present invention, the fan efficiency was improved by 17% with respect to that of the comparative example.

TABLE 1 Maximum Motor Power fan current consumption efficiency Combination of motors (A) (W) (%) Comparative Single-phase motors 1.035 12.4 30.7 example were connected Practical Three-phase motor 0.966 11.6 35.8 example and single-phase motor were connected

FIG. 4 shows P-Q characteristic curves (horizontal axis: flow rate, left vertical axis: static pressure) and a relationship between the flow rate (horizontal axis) and the rotation speed (right vertical axis) relating to the practical example and the comparative example. In the P-Q characteristic curves shown in FIG. 4, the curve 1 (solid line) is for the practical example, and the curve 2 (dashed line) is for the comparative example.

As can be seen in the P-Q characteristic curves, there was little difference between the practical example and the comparative example when the static pressure was zero, that is, when the flow rate was maximum. However, in practical use, axial-flow fan devices are generally driven under conditions between the maximum static pressure and the maximum flow rate. In these conditions of practical driving, the flow rate of the practical example was greater than that of the comparative example at any static pressure in the vertical axis on the left side. Accordingly, the P-Q characteristic (relationship between the flow rate and the static pressure) was improved in the practical example.

The reference numerals 3 and 4 in the graph of FIG. 4 represent curves based on the vertical axis on the right side. Each of the curves represents change of the rotation speed of the motor in the gas outlet side when the flow rate was increased while the motor in the gas intake side was rotated by performing rotation speed control. In the practical example (solid line with reference numeral 3), the rotation speed of the motor in the gas outlet side did not change even when the flow rate was increased, whereby loss of the electric power was slight. On the other hand, since the comparative example (dashed line with reference numeral 4) had the single-phase motor in both two axial-flow fan units, the rotation speed of the motor in the gas outlet side did not become constant even when the rotation speed control of the motor in the gas intake side was performed. Thus, loss of the electric power was greater than that of the practical example. These results indicate that the power consumption of the practical example is less than that of the comparative example.

Advantages

As described above, in the embodiment of the present invention, the counter-rotating axial-flow fan device includes a first axial-flow fan unit in the gas intake side and a second axial-flow fan unit in the gas outlet side, which are connected in series. In addition, one of the first and the second axial-flow fan units is driven by a brushless DC motor in the form of a single-phase motor, and the other is driven by a brushless DC motor in the form of a three-phase motor. Accordingly, a counter-rotating axial-flow fan device, which requires less power consumption to run and has a better flow rate-static pressure characteristic than ever before, is provided at low cost. That is, the production cost is reduced compared with a case of connecting two three-phase motors, and the flow rate is increased compared with a case of connecting two single-phase motors without increasing the power consumption.

Other Embodiments

In one embodiment, the motor in the gas intake side may be a single-phase motor, and the motor in the gas outlet side may be a three-phase motor. In this case, the three-phase motor in the gas outlet side is also driven by controlling the rotation speed thereof, and the single-phase motor in the gas intake side is also driven under predetermined conditions. The embodiment of the present invention is not limited to each of the above embodiments and may include various modifications that can be anticipated by one skilled in the art. The effects of the present invention are also not limited to the descriptions above. That is, various additions, changes, and partial deletions can be performed in a range that does not exceed the general concept and object of the present invention, which are derived from the descriptions recited in the Claims and equivalents thereof.

The present invention can be utilized for outer rotor brushless motors. 

What is claimed is:
 1. A counter-rotating axial-flow fan device comprising: a first axial-flow fan unit including a plurality of first blades and a three-phase motor for rotating the first blades in a first direction; and a second axial-flow fan unit including a plurality of second blades and a single-phase motor for rotating the second blades in a direction opposite to the first direction, the second axial-flow fan unit connected with the first axial-flow fan unit in series.
 2. The counter-rotating axial-flow fan device according to claim 1, wherein the three-phase motor is driven by controlling a rotation speed thereof.
 3. The counter-rotating axial-flow fan device according to claim 2, wherein the first axial-flow fan unit is arranged at a gas intake side of the counter-rotating axial-flow fan device.
 4. The counter-rotating axial-flow fan device according to claim 3, wherein the number of first blades in the first axial-flow fan unit is N and the number of second blades in the second axial-flow fan unit is M, and N is greater than M.
 5. The counter-rotating axial-flow fan device according to claim 3, wherein the single-phase motor of the second axial-flow fan unit is driven at a constant frequency and at a constant voltage.
 6. The counter-rotating axial-flow fan device according to claim 5, wherein the three-phase motor and the single-phase motor are driven at the same voltage.
 7. The counter-rotating axial-flow fan device according to claim 4, wherein the single-phase motor of the second axial-flow fan unit is driven at a constant frequency and at a constant voltage.
 8. The counter-rotating axial-flow fan device according to claim 7, wherein the three-phase motor and the single-phase motor are driven at the same voltage. 